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CHAPTER 2
STUDY AREA : VEMBANAD LAKE
2.1 INTRODUCTION
Kerala, cradled between the rugged ranges of Western Ghats on the
eastern border and Arabian Sea on the western border, has a unique
physiographic setting in the Indian Union. Several minor rivers originate from
the Western Ghats enhance the greenery and natural scenario of Kerala. This
strip of land has a coast that runs some 590 km in length and is bestowed with
coastal landforms such as a chain of brackish lagoons, estuaries, islands,
marshlands, flood plains and alluvial plains. About 16.4% and 54.2% of
landforms are within 0–10m and 10–300m elevation from mean sea level,
which are comprised of coastal plains and lagoons (Menon et al 2000).
The Vembanad Lake system that lies in the above category is the
largest estuarine-lagoon system in Kerala. This lake consists of a complex
system of backwaters, marshes, small islands, mangrove forests, and a
network of canals. Considering its ecological significance and high
biodiversity, it had been designated as the Ramsar Site-1214 at the
Convention on Wetlands organized by the UNESCO in the Iranian city of
Ramsar in 1981. Besides, it is classified as an “Ecologically Sensitive Zone”
as per the Environmental Protection Act 1985 (29 of 1986), by the Ministry of
Environment and Forests, India (Subramanian et al 2002). In and around this
lake is one of the highly populated coastal zones, where people depend
directly or indirectly upon this ecosystem for their livelihood. It houses the
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second largest port (Kochi Port- established 1936) in the west coast of India,
and the recently added Vallarpadam Container Terminal which functions as a
nerve centre for distribution of goods and is of high economic importance.
2.2 GEOGRAPHY
Vembanad Lake situated between Lat. 9º30 46 –10º11 11 N and
Long. 76º09 48 –76º25 45 E is distinguished by its long axes running parallel
to the coast and is separated from the sea by barrier spits interrupted by tidal
passes. This oxbow shaped lake extends for a distance of 96 km from
Azheekode in the north to Alappuzha in the south with a Northwest–
Southeast orientation (Figure 2.1). It is spread across three central districts of
Kerala, viz, Ernakulam in the north, Kottayam in the east and Alappuzha in
the south and covers an area of 241 km2(Subramanian et al 2002).
Figure 2.1 Location map of Vembanad Lake system
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The lake is connected to the Arabian Sea in the west through two
inlets, with one channel at Kochi (400 m) and another channel further north at
Azheekode (250 m). The lake consists of two major arms, i) Northern arm
(Kochi barmouth to Azheekode barmouth) which is 32 km in length and
ii) Southern arm (Kochi barmouth to Alappuzha) which is 64 km in length.
Width of the lake is generally more (0.8-6.9 km) towards southern arm but
becomes narrow (0.05-0.5 km) towards northern arm. The average depth of
the lake is 2.1 m and it occupies a volume of 0.55 km3 (Gopalan et al 1983).
The bathymetry varies considerably from place to place. In most of the places,
the depth ranges from 2-6 m except in the main channel which is used for
navigational purposes where the depth is 10-13 m (Qasim 2003). The three
dredged navigational channels are: main approach channel (10 km) oriented
along the east–west direction and two inner channels located on either side of
the Willingdon Island, i.e. Ernakulam channel (5 km) on eastern part of
Willingdon Island and Mattancherry channel (3 km) on western part of
Willingdon Island.
Two artificial hydraulic barriers were constructed at
Thanneermukkom (43 km south of Kochi inlet) and Pathalam (28 km
northeast of Kochi inlet) respectively. Thanneermukkom bund is 1447 m
long. It was built in the southern arm in 1974 and made functional in 1976.
The bund acts as a barrier which partially cuts off tidal water causing the
system to behave as two entirely different ecosystems with the brackish Kochi
backwaters (Thanneermukkom bund to Azheekode) and the freshwater lake
(Thanneermukkom bund to Alappuzha) (Gopalan et al 1983). Pathalam bund
is a temporary barrage erected only during the dry season. The northern arm
consists of islands like Vypeen, Vallarpadam and Bolghatty whereas
Willingdon, Perumbalam, Kumbalam and Pathiramanal are distributed along
the southern arm. Many small islands are scattered across the lake.
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2.3 GEOLOGY
The state of Kerala is covered mainly by four major rock units
namely precambrian crystallines, tertiary sedimentaries, laterites and the
recent to sub-recent sediments. The coastal plain of the region is of recent
geological origin, with its formation dating back to the early tertiary period,
whereas sedimentary formations on the coast are recent and sub-recent. The
lake was formed due to the initial tectonic movement followed by
sedimentation processes affected by waves and currents from the sea (Mallik
and Suchindan 1984). The present configuration of the lake was shaped
during fourteenth century A.D. following a catastrophic flood modifying the
drainage area of the rivers. The formation of parts of the present coastal
districts like Ernakulam and Alappuzha and the separation of this distinct
body of water from the sea happened after the intense flood in 1341 A.D.
(Gopalan et al 1983). Figure 2.2 illustrates the morphological changes in the
lake for the past few centuries, which has suffered severe shrinkages over the
years.
Figure 2.2 Morphological change of Vembanad Lake over centuries
(Source: Balachandran 2007)
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Kerala consists of mainly 10 broad groups of soils, tertiary,
quaternary sediments and offshore sediments in the Kerala-Laccadive basin
mixed with laterite. Lateritic and red soils cover the major portion of the
drainage basin of lake. Kaolinite, montmorillonite and illite are the major clay
mineral deposition in the bed of the lake, influenced by the riverine inputs
(Soman 1997).
2.4 LANDUSE
The land use/land cover map for the study area during the year
2008 is shown in Figure 2.3. Satellite images (IRS1C/1D) and Survey of India
toposheets were used in the preparation of map. The area around the lake
comprises a variety of unevenly distributed landforms under thirteen main
classes. These include mudflats, cropland, plantations, fallow land, sandy
beach, water logged area, settlement with vegetation, settlement and
industries. Human settlement is distributed all along the banks of study region
and is dense in the Kochi area. Population density (2011 census) in the study
region is higher (1103/km2) compared to the national average (382/km
2), and
is one of the most populated coastal zones of the world.
Of the total mapped area of 1989 km2, cropland consists of 15.3%.
Rice cultivation is one of the major occupations in this region and nearby
districts. Major share of cultivation land was mainly reclaimed from the lake
area during the last decades (Balachandran 2007). Plantations in the nearby
region occupy 7.1% of the land. The dominant plantations are of coconut and
tapioca while banana, cereals, millets, red gram, groundnut and papaya are
grown successfully as intercrops. Water body area covers 14% with a
seasonal waterlogged area of 4.6% and mudflat area <1% during the
monsoon. Settlement and settlement with vegetation cover 9.1% and 43.7% of
the total area respectively. Most of the settlements that are distributed along
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the banks of the lake are associated with vegetation. Fallow land and sandy
beach occupy 1.1% and <1% respectively. Mangrove patches are also seen in
a very small area. Industries are mainly concentrated in the northern part of
the lake and on the riverbanks. Developmental activities in this area cause
changes and stress the land use pattern in this region.
Figure 2.3 Landuse map of the Vembanad Lake
2.5 METEOROLOGICAL FACTORS
The area experiences a more or less uniform temperature
throughout the year with less seasonal variations. High temperatures occur
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during March–May varying from 30-34ºC and are lowest in December
22-24°C. The study region has the highest percentage of humidity in air
(70-90%). Humidity values are high all through the year, with lower values
during winter months and higher during the monsoon period.
The speed and direction of winds in the study region was found to
be regulated by season and by the temperature differences between land and
sea. The wind direction remains predominantly west to southwest during
southwest monsoon (June-September). From October to May, wind direction
changes from northeast in the morning hours to west during the afternoon and
evening. Southwest monsoon winds of marine origin are stronger than those
of continental origin of the northeast monsoon. Land breeze is not dominant
during June–December, but shows some influence during the summer.
The presence of Western Ghats, which obstruct the southwest
monsoon winds, results heavy rainfall in this region. Kerala receives heavy
rainfall for major part of the year and the mean climatic conditions can be
separated into two; i) dry season (Non-monsoon), which stretches from
approximately January to May and ii) rainy season in two phases – the first
from June to September (Southwest monsoon) and the second, from October
to December (Northeast monsoon). The total annual average rainfall of the
region is 320 cm (Qasim 2003). The climate is typical of the tropics with
southwest monsoon yielding 60% of the total rainfall and northeast monsoon
yielding 25%.
2.6 HYDROLOGICAL FACTORS
2.6.1 River Systems
The rivers joining the Vembanad Lake are small compared to other
major rivers in the Indian sub continent. Six perennial rivers, which originate
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from the Western Ghats flow westwards and drain into the lake before joining
the Arabian Sea. The rivers are Achenkoil (128 km), Pamba (176 km),
Manimala (90 km), Meenachil (78 km), and Muvattuppuzha (121 km) which
join at southern arm of the lake and a branch of Periyar (244 km) which joins
at the northern arm (Basak 1995). Combined drainage area of the six rivers is
12,724 km2 (Basak 1995). Drainage areas of these rivers are variable
(Figure 2.4a) depending on the land use pattern, habitation, nature of
vegetation, establishment of industrial units and other human activities. A
graphical representation of the individual river drainage areas is provided in
Figure 2.4b.
Periyar river bifurcates into two at Alwaye, one branch which
discharges nearly half of the river drains directly into the Arabian sea at
Azheekode barmouth whereas the other branch which flows toward Kochi
barmouth passes through the industrial belt at Eloor and discharges into the
Vembanad Lake. Muvattupuzha River discharges into the Kochi backwater
region between the Thanneermukkom bund and Kochi barmouth. Among the
remaining four rivers, Meenachil joins the middle east of the Vembanad Lake
after the bund while Manimala, Achankovil and Pamba join the extreme south
of the lake in Alappuzha.
Nearly 33% of the total river discharge into the estuary is from the
Periyar, which is the longest and has largest catchment area, and drains the
highest amount of water into the lake. Percentage contribution of water input
to the lake from Muvattupuzha, Achenkovil, Pampa, Meenachil and
Manimala (Srinivas et al 2003a) are shown in Figure 2.4c. Monsoonal flows
through the rivers of Kerala show strong seasonal characteristics during June
to the December. On the other hand, summer flow in the rivers forms only a
small fraction of the total runoff. More than 60% of the river discharge
(2.0 x 1010
m3
yr-1
) occurs during the southwest monsoon, 10-25% during the
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northeast monsoon and the remaining during the rest of the year
(Srinivas et al 2003b).
Figure 2.4 a) Drainage area of rivers joining the Vembanad Lake
b) Drainage area graph in (km2)
c) Percentage contribution of river water input to
Vembanad Lake
2.6.2 Tides
Every estuary has its own tidal characteristics, which influences the
mixing, circulation and hydrodynamic processes of the system. In Vembanad
Lake tides enter and exit through two perennially open narrow inlets with
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cross sectional area of 4234 m2 at Kochi mouth (Joseph 1996) and the
Azheekode mouth of lesser area. The tides are usually mixed semi-diurnal
with two high and two low waters that occur daily with inequalities in range
and time. The maximum amplitude is 1 m, and the magnitude of tides
progressively decreases with increase in the distance from the barmouth. The
flood and ebb currents are comparatively higher in the Ernakulam channel than
in the Mattanchery channel (Strikwerda 2004). The northern arm frequently
develops flow-restrictions due to converging tides entering from two adjacent
inlets, whereas tidal amplification is noticed in the southern arm
(Balachandran et al 2008). During summer, seawater reaches the head of the
estuary (Alappuzha), but is restricted to 25 km during monsoon.
2.6.3 Hydrodynamics
Vembanad Lake is a positive type estuary with the riverine inflow
and precipitation exceeding evaporation. Intermixing of tidal water and river
water gives the lake the characteristics of a tropical estuary (Balchand and
Nair 1994). The topography of the lake regulates the circulation pattern,
which behaves distinctly in the two arms of the lake. There is a significant
difference in the runoff and tidal influence during different seasons and
generally is referred to as monsoonal estuary; the west coast of India mainly
consists of this type of tropical monsoonal estuaries (Shetye et al 2007).
During the monsoon, the system conditions are dominantly of a freshwater
body and after that, the system gradually changes into brackish water with
marine conditions dominating during summer.
Fluvial supply from rivers result in high siltation and the sediment
flux from the catchments is about 32 x 106 tonnes yr
-1 (Thomson 2002).
Hydrodynamic conditions regulate the mode of accretion and siltation, which
causes shrinkage of the estuary. The exchange volume of the estuary has also
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been reduced by 90 Mm3 per tidal cycle from 1960 to 1985 (Balachandran
2007). In addition, hydrodynamic aspects of the system are influenced by
various anthropogenic activities and its dynamics are not completely
understood.
2.7 FLORA AND FAUNA
This Ramsar site No.1214 has a unique environmental habitat
which supports rich and diverse species of flora and fauna. Both freshwater
and saline water species are present in this tropical estuary, and consist of 194
species of phytoplankton and 135 species of zooplankton (Subramanian et al
2002). Diatoms and Copepods are the dominant groups among the
phytoplankton and zooplankton community respectively. The major aquatic
plants present in this lake include Eichhornia crassipes (water hyacinth) and
Salvinia molesta (giant salvinia, kariba weed) which are widely distributed
and are a threat to the ecosystem. Small isolated patches of mangrove
vegetation are present at Kumarakom, Vypeen, Kannamali and Chettuva
regions of this estuary.
Faunal diversity includes a large variety of fishes, prawns, clams,
reptiles and birds. Fishes present in this lake are mainly oligohaline and
estuarine fishes which migrate from the Arabian Sea to the lake and vice
versa. Marine penaeid prawns, clams like Villorita cyprinoids and Mertrix
meretrix are exploited more from this region of the Kerala coast. Polychaetes,
crustaceans and molluscs are the major members of benthic community in the
lake. This ecosystem supports the third largest population of waterfowl in
India during the winter months (Rajan et al 2008). Numerous species of
resident and migratory birds are found visiting this area for breeding and
feeding. Rich insect biodiversity is also found with butterflies forming the
majority.
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2.8 ECONOMIC SIGNIFICANCE
2.8.1 Navigation
The Port of Kochi, a natural port/harbour located near the Kochi
barmouth, which handled about 15.7 x 106 tonnes during 2007-08
(www.worldportsource.com/ports/IND_Port_of_Cochin), is busy throughout
the year. Recently, an international container trans-shipment terminal facility
is being developed at Vallarpadam, described as a milestone in infrastructure
development logistics. This has placed India in a key position in the world
maritime map. Inland navigation through the national waterway (Kollam-
Kottappuram segment) and lower reaches of rivers is a major means of
transportation in this area.
2.8.2 Tourism
Extensive network of rivers, lakes, canals, and lagoons fringed by
lush green coconut groves and paddy fields, harbouring rich avifauna; water
sports like the famous snake-boat race and the calm and pleasant environment
with boating facilities makes Vembanad Lake one of the top 50 destinations
on the global tourism map. This helps the flourishing tourism industry in
Kumarakom, Alappuzha and Kochi region and also provides employment
opportunities. However, tourism facilities like resorts and hotels are being
developed without any concern for the natural system increasing the pressure
on the ecosystem.
2.8.3 Fisheries
Vembanad Lake supports rich fishery resources and provides
feeding, spawning and nursery grounds for large numbers of commercial fish
and shellfish. About 32.5% of the fisherman population of the state is
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concentrated on the banks of the lake. Lake production per year consists of
5000 tonnes of fish and almost same quantity of prawns, and 300-400 tonnes
of giant fresh water prawn. Over fishing, use of banned fishing gears and
massive reclamation has resulted in the decline of the fishing area and has
also affected the productivity of fishing grounds. Unnithan et al (2001)
reported decline in annual landing of fisheries from 16,000 tonnes per year
during late seventies to about 7,200 tonnes in recent years. Further confirms
by the decrease in fish species from 150 to 62 in the recent survey on 2008 by
Priyadharshanan and Latha (2009).
2.8.4 Clam Mining
Clams are widely distributed and form vast deposits between the
Pathiramanal Island and Vaikom region. Clam deposits are quarried by
various industries. This is in addition to live clam collection, one of the major
occupations of women and children in this area. Clam meat forms a cheap
protein source for the poor people of this locality. There is a decline in clam
shell production and landing from 2500 tonnes to 1300 tonnes (Arun 2005).
Uncontrolled mining of shells from the lake is also posing a threat to the
ecosystem.
2.8.5 Coir Industry
About 0.35 million workers mainly from socially and economically
backward communities in this region depend on the coir cottage industry.
Brackish waters of the Vembanad Lake are used as coconut husk retting yards
by coir manufacturing industries and Alappuzha acts as the nerve centre of
Kerala’s coir industry. It is important in Kerala’s economy and accounts for
70% production of the coir products in India.
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2.9 ANTHROPOGENIC INTERVENTION AND THREATS
Human intervention started in 1888 in the form of land being
reclaimed for agriculture in the southern parts of the lake (Balachandran
2007). Then, during 1920-1936 there was reclamation and creation of
Willingdon Island and dredging to maintain the shipping channel for the
harbour. Subsequently during 1940’s, industries were allowed to be
established along the upper reaches of the estuary which led to intense
reclamation for human settlements since 1940. During 1955, Thottapally
spillway was constructed to divert the floodwaters of Achankovil, Manimala,
Pamba and Meenachil directly to sea. Thanneermukkom Bund (1976) was
built to improve agricultural output, and a temporary barrage in Pathalam
bund was constructed on the Eloor branch of Periyar River since 1981.
During 2011, the first phase of the International Container
Transhipment Terminal at Vallarpadam was constructed to handle
international cargo. The region is still witnessing many engineering
modifications like construction of houses/factories on reclaimed land,
waterways development, erection of bridges and deepening of shipping
channels, required to support rapid economic development. All these
anthropogenic activities have led to the shrinking of the water spread area of
the backwaters from 365 km2 to 256 km
2 (Balachandran 2007). These
interventions have had significant effect on the hydrodynamic aspects of the
system leading to dispersion of pollution and diminishing of the bioresources
of the system.
2.9.1 Agricultural Activities
Rising requirement for food has resulted in intense agriculture in
the Kuttanad (rice bowl of Kerala) region. The fertilizer consumption in
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Kuttanad region alone is reported to be 20,239 tonnes yr-1
(Nair 2002). A
large amount of chemical fertilizer has been added to the other variety of
plantation and crops in the nearby regions to maintain high production. These
all seems to an increase in use of nitrogen/phosphorus containing fertilizers in
these areas. Intense agricultural practices are responsible for the reclamation
of lake area, inputs of fertilizers and pesticides and fall in soil fertility.
2.9.2 Domestic Sewage
Industrialization and commercialization attracts a lot of migrants
and this increase in population has resulted in the enhanced discharge of
260 m3
d-1
of organic waste in to the Cochin estuary (Balachandran et al
2005). Urban sewage from Kochi city including slaughter house wastes, and
wastes from the markets and hospitals as well as domestic wastes reach the
lake through the network of natural and artificial canals. Discharge from
motor boats, resorts and houseboats directly into the lake are a major source
of organic pollutants.
2.9.3 Artificial / Engineering Construction
Thanneermukkom bund, constructed to prevent salinity intrusion
into Kuttanad farmland for high crop yield, has resulted in the reduction of
population of fish and shrimps. This artificial barrier produces negative
impacts like arresting the tidal flushing which results in the trapping of
agricultural pollutants, increased growth of water hyacinth and severe
environmental degradation. Drastic ecological changes have been reported
particularly south of the Thanneermukkom bund, thereby affecting the
ecology and distribution of the living resources in the estuary (Menon et al
2000, Arun 2005). The Kochi shipyard and port activities release sizeable
quantities of waste oil, paints, metal and paint scrapings. Various engineering
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activities by Vallarpadam terminal and the annual dredging of Kochi
navigation channel (l0 x 106 m
3) have adverse effects on the circulation
pattern, sedimentation rate and the ecology in the estuarine region (Rasheed
1997).
2.9.4 Industrial Pollution
Kochi, the industrial capital of Kerala, has a lion’s share of
chemical industries, which are situated on the banks of river Periyar and also
in the upper and mid reaches of the system. The industrial typology includes
fertilizer, pesticides, radioactive mineral processing, chemicals and allied
industries, petroleum refining and heavy metal processing, food and drug
manufacturing and fish processing. It is estimated that nearly 104 million
litres of partially treated and untreated industrial effluents generated every day
by various industries (Menon et al 2000, Balachandran et al 2006).
Small-scale industries on the banks of the lake like coir industry, where
processing is carried out through traditional retting practices and fermentation
of coconut husk contributes to the organic load entering the system.
Overall, the Vembanad Lake, an economically important system is
undergoing a great deal of environmental alterations due to various activities
induced by economic gain and development. The quest for economic gain
without concern for the environment has resulted in adverse environmental
impacts and a fast declining ecosystem. This is mainly caused by improper
management and lack of awareness, which provide challenges for coastal
managers and policy makers in future.